In the manufacture of coke from coal a batch of coal is charged to a coking oven where it is subjected to a high temperature at which volatiles are driven off from the coal. A typical system includes a battery of coke ovens which contains a large number of coking chambers disposed side-by-side along the length of the oven. For the most part charging of the chambers is performed mechanically by dumping coal from a larry car into each chamber through a plurality of vertically facing charging openings located in the top of each chamber.
In more recent years a new method for charging of the chambers has been developed which effects charging through enclosed pipelines in which dried, preheated coal particles are transported by an inert pressurized conveying or carrying gas into each coke oven chamber. The carrier gas, such as superheated steam or coke oven gas, may be introduced into the pipeline along its length through a number of strategically placed jets which propel the coal in the desired direction and which prevent the coal from settling to the bottom of the pipeline. Usually the coal particles to be delivered to one or more ovens are fed into a generally horizontal main pipeline which extends the length of the oven at an elevation somewhat above the top of the oven. For each chamber there is provided a branch pipeline which connects at its upstream end with the main pipeline by means of a diverter valve. The downstream or discharge end of each branch pipeline is a straight length which passes through the top or the end wall of the respective coking chamber at one end thereof at an angle of about 15.degree. to 30.degree. from the horizontal. The branch pipeline is curved just prior to the straight discharge end portion to induce an internal flow pattern which causes some separation between the coal and the carrier gas. A portion of the carrier gas is usually tapped from the pipeline at this point in order to increase the coal to gas ratio of the mixture entering the chamber. A gas take-off pipe extends through the top of the chamber at the end thereof opposite the location of the coal inlet pipeline.
A typical coke oven of contemporary design is of a size to hold a charge of from about 15 to 35 tons or more of coal and there may be 20 to 90 such chambers in a given coke oven battery. Such chambers, which have a volumetric capacity of from about 600-1600 cubic feet, are approximately 35 to 50 feet long, from 11 to 22 feet high and approximately 11/2 feet wide. The feed rate into the oven typically may range from about 2 to 6 tons per minute. The coal particles after being preheated to 250.degree. F.-700.degree. F. are introduced into the main pipeline and are conveyed therealong at a rate in the range of about 10-200 ft/sec by steam at 4-50 psig. The weight ratio of coal to steam typically is in the range 20 to 350 to 1 at the upstream portion of the main pipeline and in the range 40 to 500 to 1 at the discharge end of the branch pipeline.
The coal is discharged into the chamber essentially in a fluidized condition and the fluidized condition is maintained for a short period of time. Disentrainment of the coal particles from the carrier gas occurs slowly, causing the fluidized mixture to flow the length of the chamber as carrier gas flows through the gas take-off pipe. Disentrainment takes place slowly enough and uniformly enough to disperse the coal particles from the entry end along the length of the chamber. On the other hand disentrainment takes place rapidly enough to avoid charging the chamber to excessive or dangerous levels and to avoid excessive carry over of coal fines in the carrier gas leaving the chamber through the gas take-off pipe.
All of the above is disclosed in more detail in U.S. Pat. Nos. 3,374,151, 3,432,398, 3,457,141, 3,523,065, 3,537,755 and 3,761,360 the specifications of which are incorporated herein by reference. U.S. Pat. No. 3,761,360 recognizes some of the problems which arise during the charging of coal by pneumatic conveying, such as the carry-over of coal fines by the carrier gas and the disability of the technique to fill the chamber to an absolutely predetermined depth completely along the length of the chamber. Reduction of the carry-over of coal fines is desirable from the economic standpoint of reducing the amount of fines which must be recycled. A uniformly full chamber is desirable from the standpoint of obtaining maximum capacity and a uniform coke product. It is generally desirable also to form a bed of coal particles which is as dense as possible and to employ as small an amount of carrier gas as possible. Higher densities are not preferable where wall pressure generated during the coking cycle is near the maximum acceptable limit for coke ovens.